Śatapatha Brāhmaṇa ("of a hundred paths") 3.6.3.8

3.6.3.8

athāptave dvitīyāmāhutiṃ juhoti | juṣāṇo apturājyasya vetu svāhetyeṣa u haivaitaduvāca rakṣobhyo vai bibhemi yathā māntarā nāṣṭrā rakṣāṃsi na hinasannevam mā kanīyāṃsameva badhātkṛtvātinayata stokameva stoko hyapturiti tametatkanīyāṃsameva badhātkṛtvātyanayantstokameva stoko hyaptū rakṣobhyo bhīṣā tasmādaptave dvitīyāmāhutiṃ juhoti

He then offers the second oblation to (Soma) the Nimble, with, 'May the Nimble graciously accept the butter, Hail!' For he (Soma) spake upon that time, 'Verily I am afraid of the Rakshas: do ye make me to be too small for their deadly shaft, so that the evil spirits (the Rakshas) shall not injure me on the way; and take me across in the form of a drop, for the drop is nimble.' And accordingly, having made him too small for the deadly shaft, they lead him safely across in the form of a drop, from fear of the Rakshas, for the drop is nimble: this is why he offers the second oblation to (Soma) the Nimble.